No one ever enters into a marriage or commited relationship with the thought that one day this might end.
However, sometimes these relationships do end.
Consider marking this change in your family with a short and simple ceremony of renewal.
This could be especially important if the relationship produced any children. It can also help the extended family - who have after all become one family through this to begin to heal and remain strong.
I think it is a joyful and wonderful thing when parents who are divorcing/separating can come together in mutual love and respect for their children and even in a sense each other. Promising one's children in a solemn ceremony that their parents will always do what is in their interest and will be supportive of them and cooperative with each other is a very great gift that can be given.
In any case I wish you the easiest of proceedings- do not let pain and animosity destroy what you love most about yourself and others in your life.
Blessed Be....